Implantable medical lead with threaded fixation

ABSTRACT

The disclosure is directed to securing electrodes of a medical lead adjacent to a target tissue site. The medical lead may include one or more threaded fixation structures disposed circumferentially about the outer surface of the lead body, or elongated member, that resembles a “screw” or “auger.” During implantation, a clinician may rotate the entire lead to “screw” the lead into the tissue of the patient until electrodes of the lead reside adjacent to a target tissue. In this manner, the threaded fixation structure secures the lead within the patient to resist lead migration and improper therapy and provide a fine adjustment for depth of placement. The threaded fixation structure may be disposed on a portion of the lead proximal to or distal to the electrodes of the lead or over the portion of the lead that includes the electrodes.

TECHNICAL FIELD

The invention relates to stimulation systems and, more particularly, tostimulation leads in stimulation systems.

BACKGROUND

Electrical stimulation systems may be used to deliver electricalstimulation therapy to patients to treat a variety of symptoms orconditions such as chronic pain, tremor, Parkinson's disease, multiplesclerosis, spinal cord injury, cerebral palsy, amyotrophic lateralsclerosis, dystonia, torticollis, epilepsy, pelvic floor disorders, orgastroparesis. An electrical stimulation system typically includes oneor more stimulation leads coupled to an external or implantableelectrical stimulator. The stimulation lead may be percutaneously orsurgically implanted in a patient on a temporary or permanent basis suchthat at least one stimulation electrode is positioned proximate to atarget stimulation site. The target stimulation site may be, forexample, a spinal cord, pelvic nerve, pudendal nerve, stomach, muscle,or within a brain or other organ of a patient. The electrodes locatedproximate to the target stimulation site may deliver stimulation therapyto the target stimulation site in the form of electrical signals.

Electrical stimulation of a sacral nerve may eliminate or reduce somepelvic floor disorders by influencing the behavior of the relevantstructures, such as the bladder, sphincter and pelvic floor muscles.Pelvic floor disorders include urinary incontinence, urinaryurge/frequency, urinary retention, pelvic pain, bowel dysfunction, andmale and female sexual dysfunction. The organs involved in bladder,bowel, and sexual function receive much of their control via the second,third, and fourth sacral nerves, commonly referred to as S2, S3 and S4respectively. Thus, in order to deliver electrical stimulation to atleast one of the S2, S3, or S4 sacral nerves, a stimulation lead isimplanted proximate to the sacral nerve(s).

Electrical stimulation of a peripheral nerve, such as stimulation of anoccipital nerve, may be used to induce paresthesia. Occipital nerves,such as a lesser occipital nerve, greater occipital nerve or thirdoccipital nerve, exit the spinal cord at the cervical region, extendupward and towards the sides of the head, and pass through muscle andfascia to the scalp. Pain caused by an occipital nerve, e.g. occipitalneuralgia, may be treated by implanting a lead proximate to theoccipital nerve to deliver stimulation therapy.

In many stimulation applications, including stimulation of a sacralnerve, it is desirable for a stimulation lead to resist migrationfollowing implantation. For example, it may be desirable for theelectrodes disposed at a distal end of the implantable medical lead toremain proximate to a target stimulation site in order to provideadequate and reliable stimulation of the target stimulation site. Insome applications, it may also be desirable for the electrodes to remainsubstantially fixed in order to maintain a minimum distance between theelectrode and a nerve in order to help prevent inflammation to the nerveand in some cases, unintended nerve damage. Securing the stimulationlead at the target stimulation site may minimize lead migration.

SUMMARY

In general, the disclosure is directed toward securing electrodes of amedical lead adjacent to a target tissue site with a threaded fixationstructure configured to engage tissue within a patient to resistmigration of the medical lead. The medical lead may be similar to a“screw” or “auger-like.” The threaded fixation structure defines one ormore threads disposed circumferentially about the outer surface of alead body. Specifically, the threads of the threaded fixation structuremay be arranged in a helical pattern. During implantation, a clinicianmay rotate the entire lead to “screw” the lead into the tissue of thepatient until electrodes of the lead reside adjacent to a target tissue.In this manner, the threaded fixation structure secures the lead withinthe patient to resist lead migration. In addition, the threaded fixationstructure may allow a fine adjustment mechanism for the depth of theelongated member within the tissue. The threaded fixation structure maybe disposed on a portion of the lead proximal to or distal to theelectrodes of the lead or over the portion of the lead that includes theelectrodes. In some cases, the entire distal end of the lead may includethe threaded fixation structure to engage a greater area of tissue. Inother embodiments, the threaded fixation structure may be used with drugdelivery catheters instead of electrical stimulation leads.

In one embodiment, the disclosure is directed to a medical lead thatincludes an elongated member having a proximal end and a distal end, atleast one stimulation electrode disposed closer to the distal end of thelead than the proximal end of the lead, and at least one threadedstructure extending around a portion of an outer surface of theelongated member and configured to engage tissue within a patient toresist migration of the medical lead.

In another embodiment, the disclosure is directed to method thatincludes inserting a medical lead into a patient, wherein the leadcomprises at least one stimulation electrode and at least one threadedfixation structure extending around a portion of an outer surface of thelead, and rotating the lead to engage the threaded fixation structurewith tissue of the patient to resist migration of the lead.

In an additional embodiment, the disclosure is directed to a system thatincludes a medical lead having an elongated member having a proximal endand a distal end, at least one stimulation electrode disposed closer tothe distal end of the lead than the proximal end of the lead, and atleast one threaded structure extending around a portion of an outersurface of the elongated member and configured to engage tissue within apatient to resist migration of the medical lead. The system alsoincludes a stimulator that delivers electrical stimulation therapy to apatient via the medical lead within the patient.

In another additional embodiment, the disclosure is directed to anapparatus that includes an elongated member having a proximal end and adistal end, a conduit disposed within the elongated member, an exit portdisposed on an outer surface of the elongated member in fluidiccommunication with the conduit, and at least one threaded fixationstructure extending around a portion of an outer surface of theelongated member and configured to engage tissue within a patient toresist migration of the medical lead.

The disclosure may provide one or more advantages. The threaded fixationstructure may be engaged to the adjacent tissue of the patient and stillallow the clinician to advance or retract the lead to finely adjust thelead position. A sheath may also be used to cover the threaded fixationstructure until the clinician desires to expose the threaded fixationstructure to the adjacent tissue, and the sheath may collapse thethreaded fixation structure to reduce the lead diameter until leadfixation is desired. In addition, the clinician may remove the lead byrotating the lead and reducing tissue trauma.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic perspective view of a therapy system including anelectrical stimulator coupled to a stimulation lead that has beenimplanted in a body of a patient proximate to a target stimulation site.

FIG. 1B is an illustration of the implantation of a stimulation lead ata location proximate to an occipital nerve.

FIG. 2 is a block diagram illustrating various components of anelectrical stimulator and an implantable lead.

FIGS. 3A and 3B are perspective drawings of a sheath that covers a leadprior to implantation and is removed after the lead is correctlypositioned in a patient.

FIGS. 4A-4C are perspective drawings illustrating exemplary stimulationleads with varying configurations of threaded fixation mechanisms.

FIGS. 5A-5B are perspective drawings illustrating exemplary stimulationleads with varying threaded fixation mechanisms over electrodes of thelead.

FIG. 6 is a perspective drawing illustrating an exemplary stimulationlead with threads from the distal tip to a location proximal toelectrodes.

FIG. 7 is a perspective drawing illustrating an exemplary stimulationlead with torsional reinforcement members within the elongated member.

FIGS. 8A and 8B are perspective drawings illustrating exemplarystimulation leads with foldable threads.

FIG. 9 is a flow diagram illustrating an exemplary process for securinga threaded lead to a tissue of a patient.

FIG. 10 is a flow diagram illustrating an exemplary process for removinga threaded lead from a tissue of a patient.

FIG. 11 is a flow diagram illustrating an exemplary process for securinga lead with folding threads to a tissue of a patient.

FIGS. 12A and 12B are perspective drawings illustrating exemplarymedical catheters with a helical threaded structure.

FIGS. 13A and 13B are cross-sectional end views of a keyed stylet andreciprocally keyed medical lead.

DETAILED DESCRIPTION

The medical leads described herein include a threaded fixation mechanismthat secures the medical lead within a tissue of a patient. The threadedfixation mechanism prevents the electrodes of the lead from migratingaway from the target stimulation tissue, which may lead to a reductionin therapy efficacy. Specifically, the threaded fixation mechanismincludes a thread structure disposed around the outer surface of theelongated member, such that the lead resembles a “screw” or “auger”device that advances or retreats when rotated. The threaded fixationmechanism may allow the clinician to finely adjust the elongated memberlocation, in contrast to other medical lead fixation structures such astines or adhesives. Generally, the threads may be arranged in a helicalpattern, but other types of thread patterns may also be used to securethe lead. Hence, the threaded fixation mechanism may be referred to as athreaded fixation structure for purposes of illustration. In addition,other non-helical thread patterns may be used in some embodiments. Thethread structure may be disposed distal to the electrodes, proximal tothe electrodes, and/or at the same axial position of the electrodes. Inaddition, in some embodiments, the threaded fixation structure may bedisposed on a tapered tip at the distal end of the elongated member tobegin the engagement and tunneling of the lead through the tissue whenthe lead is rotated to secure the threaded fixation structure.

In some embodiments, the thread structure may not engage the adjacenttissue until the user, e.g. a clinician, desires the structure to do so.For example, a sheath may be configured to cover the elongated memberand thread structure for lead insertion and be removed to allow thethreaded fixation structure to contact the adjacent tissue. In addition,the thread structure may fold down against the elongated member outersurface when constricted by the sheath. When the clinician removes thesheath, the threaded fixation structure extends away from the elongatedmember and returns to its original thread shape to secure the lead. Inthis case, the thread structure may have elastic, super-elastic, orshape memory properties that cause it to assume an extended positionwhen a sheath or other restraint mechanism is removed to expose thethread structure.

Alternatively, the medical lead may not include electrodes on theelongated member. In this case, the medical lead may be a catheter thatdelivers a therapeutic agent through one or more lumens in the elongatedmember, while the threaded fixation structure secures the location ofthe catheter. The lumen may end at one or more exit ports near thedistal end of the elongated member, and the exit ports may be disposedin an axial or longitudinal outer surface of the elongated member.

FIG. 1A a schematic perspective view of therapy system 10, whichincludes electrical stimulator 12 coupled to stimulation lead 14, whichhas been implanted in body 16 of a patient proximate to targetstimulation site 18. Electrical stimulator 12 provides a programmablestimulation signal (e.g., in the form of electrical pulses orsubstantially continuous-time signals) that is delivered to targetstimulation site 18 by stimulation lead 14, and more particularly, viaone or more stimulation electrodes carried by lead 14. Electricalstimulator 12 may be either implantable or external. For example,electrical stimulator 12 may be subcutaneously implanted in the body ofa patient 16 (e.g., in a chest cavity, lower back, lower abdomen, orbuttocks of patient 16). Electrical stimulator 12 may also be referredto as a pulse or signal generator, and in the embodiment shown in FIG.1A, electrical stimulator 12 may also be referred to as aneurostimulator. In some embodiments, lead 14 may also carry one or moresense electrodes to permit stimulator 12 to sense electrical signalsfrom target stimulation site 18. Furthermore, in some embodiments,stimulator 12 may be coupled to two or more leads, e.g., for bilateralor multi-lateral stimulation.

Lead 14 further includes a lead body, or elongated member, and one ormore threaded fixation structures (not shown in FIG. 1) which engagewith tissue proximate to target stimulation site 18 to substantially fixa position of lead 14 proximate to target stimulation site 18. Thethreaded fixation structure is rotated during implantation to engagewith tissue adjacent to target stimulation site 18. Proximal end 14A oflead 14 may be both electrically and mechanically coupled to connector13 of stimulator 12 either directly or via a lead extension. Inparticular, lead 14 may include electrical contacts near proximal end14A to electrically connect conductors disposed within the elongatedmember to stimulation electrodes (and sense electrodes, if present) at aposition adjacent to distal end 14B of lead 14 to stimulator 12. Lead 14may be connected directly or indirectly (e.g., via a lead extension) tostimulator 12.

In the example embodiment of therapy system 10 shown in FIG. 1A, targetstimulation site 18 is proximate to the S3 sacral nerve, and lead 14 hasbeen introduced into the S3 sacral foramen 22 of sacrum 24 to access theS3 sacral nerve. Stimulation of the S3 sacral nerve may help treatpelvic floor disorders, urinary control disorders, fecal controldisorders, interstitial cystitis, sexual dysfunction, and pelvic pain.Therapy system 10, however, is useful in other stimulation applications.Thus, in alternate embodiments, target stimulation site 18 may be alocation proximate to any of the other sacral nerves in body 16 or anyother suitable nerve in body 16, which may be selected based on, forexample, a therapy program selected for a particular patient. Forexample, in other embodiments, therapy system 10 may be used to deliverstimulation therapy to pudendal nerves, perineal nerves, or other areasof the nervous system, in which cases, lead 14 would be implanted andsubstantially fixed proximate to the respective nerve. As furtheralternatives, lead 14 may be positioned for temporary or chronic spinalcord stimulation for the treatment of pain, for peripheral neuropathy orpost-operative pain mitigation, ilioinguinal nerve stimulation,intercostal nerve stimulation, gastric stimulation for the treatment ofgastric mobility disorders and obesity, muscle stimulation (e.g.,functional electrical stimulation (FES) of muscles), for mitigation ofother peripheral and localized pain (e.g., leg pain or back pain), orfor deep brain stimulation to treat movement disorders and otherneurological disorders. Accordingly, although sacral nerve stimulationwill be described herein for purposes of illustration, a stimulationlead 14 in accordance with the invention may be adapted for applicationto a variety of electrical stimulation applications.

Migration of lead 14 following implantation may be undesirable, and mayhave detrimental effects on the quality of therapy delivered to apatient 16. For example, migration of lead 10 may cause displacement ofelectrodes carried by lead 14 to a target stimulation site 18. As aresult, the electrodes may not be properly positioned to deliver thetherapy, possibly undermining therapeutic efficacy of the stimulationtherapy from system 10. Substantially fixing lead 14 to surroundingtissue may help discourage lead 14 from migrating from targetstimulation site 18 following implantation, which may ultimately helpavoid harmful effects that may result from a migrating stimulation lead14.

To that end, the invention provides lead 14 with a thread structure (notshown in FIG. 1) disposed around the elongated member of lead 14 toprovide fixation between lead 14 and tissue surrounding lead 14, such astissue within sacrum 16 in the example of FIG. 1A. The thread structuremay have a helical pattern that permits lead 14 to be, in effect,screwed into a tissue site. In comparison to some existing methods offixing implanted medical leads, such as suturing lead 14 to surroundingtissue or applying a cuff electrode, using a threaded fixation structureto secure lead 14 in patient 16 may be beneficial in a minimallyinvasive surgery, which may allow for reduced pain and discomfort forpatient 16 relative to invasive surgery, as well as a quicker recoverytime. As described in further detail below, the threaded fixationstructure is disposed around the outer surface of the elongated bodynear the distal end of lead 14 and configured to engage with theadjacent tissue to prevent lead 14 movement.

Implanting lead 14 with the threaded fixation structure may be completedvia a few methods. First, the clinician may rotate lead 14 to advancelead 14 toward target stimulation sire 18 and utilize the threadedfixation structure to engage the adjacent tissue. Second, a sheath (notshown in FIG. 1A) may be used initially to cover lead 14 and theincluded threaded fixation structure to allow the clinician to insertlead 14 into patient 16 until direct insertion is no longer possible. Atthis point, the clinician may remove the sheath to expose the threadedfixation structure and then rotate lead 14 to advance lead 14 the restof the distance towards target stimulation site 18.

The rotation of lead 14 may be achieved directly by rotating the leadbody, or by a stylet or other device that is inserted into an innerlumen of the lead to engage the lead. In some embodiments, the styletmay have a keyed structure, such as one or more longitudinal flanges,ribs, teeth or grooves that engage reciprocal structure in the innerlumen of the lead. For example, a keyed stylet may be inserted to engagethe distal end of the lead and lock into interior grooves or teeth tofacilitate the rotation of the lead. In particular, reciprocal teeth orgrooves, or the like, may rotationally bear against each other such thatrotation of the stylet causes rotation of the lead in the samedirection.

In addition, the threaded fixation structure may be foldable against theelongated member of lead 14 when covered by the sheath. When the sheathis removed, the threaded fixation structure may stand up, or extend,away from the elongated member to its original shape. The clinician maythen rotate lead 14 to advance lead 14 to target stimulation site 18. Ineither case, the thread tends to “bite” into the surrounding tissue toresist migration of the lead from the target stimulation site.

Therapy system 10 also may include a clinician programmer 26 and apatient programmer 28. Clinician programmer 26 may be a handheldcomputing device that permits a clinician to program stimulation therapyfor patient 16, e.g., using input keys and a display. For example, usingclinician programmer 26, the clinician may specify stimulationparameters for use in delivery of stimulation therapy. Clinicianprogrammer 26 supports telemetry (e.g., radio frequency telemetry) withstimulator 12 to download stimulation parameters and, optionally, uploadoperational or physiological data stored by stimulator 12. In thismanner, the clinician may periodically interrogate stimulator 12 toevaluate efficacy and, if necessary, modifies the stimulationparameters.

Like clinician programmer 26, patient programmer 28 may be a handheldcomputing device. Patient programmer 28 may also include a display andinput keys to allow patient 16 to interact with patient programmer 28and implantable stimulator 12. In this manner, patient programmer 28provides patient 16 with an interface for control of stimulation therapyby stimulator 12. For example, patient 16 may use patient programmer 28to start, stop or adjust stimulation therapy. In particular, patientprogrammer 28 may permit patient 16 to adjust stimulation parameterssuch as duration, amplitude, pulse width and pulse rate, within anadjustment range specified by the clinician via clinician programmer 28,or select from a library of stored stimulation therapy programs.

Stimulator 12, clinician programmer 26, and patient programmer 28 maycommunicate via cables or a wireless communication, as shown in FIG. 2.Clinician programmer 26 and patient programmer 28 may, for example,communicate via wireless communication with stimulator 12 using radiofrequency (RF) telemetry techniques known in the art. Clinicianprogrammer 26 and patient programmer 28 also may communicate with eachother using any of a variety of local wireless communication techniques,such as RF communication according to the 802.11 or Bluetoothspecification sets, or other standard or proprietary telemetryprotocols.

FIG. 1B is a conceptual illustration of an alternative implantation siteto the implantation of FIG. 1A. Therapy system 10 may also be used toprovide stimulation therapy to other nerves of a patient 16. Forexample, as shown in FIG. 1B, lead 14 may be implanted and fixated withthe two or more threaded fixation members proximate to an occipitalregion 29 of patient 30 for stimulation of one or more occipital nerves.In particular, lead 14 may be implanted proximate to lesser occipitalnerve 32, greater occipital nerve 34, and third occipital nerve 36. InFIG. 1B, lead 14 is aligned to be introduced into introducer needle 38and implanted and anchored or fixated with fixation elements proximateto occipital region 29 of patient 30 for stimulation of one or moreoccipital nerves 32, 34, and/or 36. A stimulator (e.g., stimulator 12 inFIG. 1A) may deliver stimulation therapy to any one or more of occipitalnerve 32, greater occipital nerve 34 or third occipital nerve 36 viaelectrodes disposed adjacent to distal end 14B of lead 14. In alternateembodiments, lead 14 may be positioned proximate to one or more otherperipheral nerves proximate to occipital nerves 32, 34, and 36 ofpatient 30, such as nerves branching from occipital nerves 32, 34, and36, as well as stimulation of any other suitable nerve, organ, muscle,muscle group or other tissue site within patient 30, such as, but notlimited to, nerves within a brain, pelvis, stomach or spinal cord ofpatient 30.

Implantation of lead 14 may involve the subcutaneous placement of lead14 transversely across one or more occipital nerves 32, 34, and/or 36that are causing patient 30 to experience pain. In one example method ofimplanting lead 14 proximate to the occipital nerve, using localanesthesia, a vertical skin incision 33 approximately two centimeters inlength is made in the neck of patient 30 lateral to the midline of thespine at the level of the C1 vertebra. The length of vertical skinincision 33 may vary depending on the particular patient. At thislocation, patient's skin and muscle are separated by a band ofconnective tissue referred to as fascia. Introducer needle 38 isintroduced into the subcutaneous tissue, superficial to the fascia andmuscle layer but below the skin. Occipital nerves 32, 34, and 36 arelocated within the cervical musculature and overlying fascia, and as aresult, introducer needle 38 and, eventually, lead 14 are insertedsuperior to occipital nerves 32, 34, and 36.

Once introducer needle 38 is fully inserted, lead 14 may be advancedthrough introducer needle 38 and positioned to allow stimulation of thelesser occipital nerve 32, greater occipital nerve 34, third occipitalnerve 36, and/or other peripheral nerves proximate to an occipitalnerve. Upon placement of lead 14, introducer needle 38 may be removed.In some embodiments, introducer needle 38 may be used to remove lead 14after stimulation therapy is no longer needed.

Accurate lead placement may affect the success of occipital nervestimulation. If lead 14 is located too deep, i.e., anterior, in thesubcutaneous tissue, patient 30 may experience muscle contractions,grabbing sensations, or burning. Such problems may additionally occur iflead 14 migrates after implantation. Furthermore, due to the location ofimplanted lead 14 on the back of patient's 30 neck, lead 14 may besubjected to pulling and stretching that may increase the chances oflead migration. For these reasons, lead 14 may employ the threadedfixation structure to secure lead 14 within patient 16. In locationsnear the skin of patient 16, the threaded fixation structure may onlyextend from the elongated body of lead 14 a small distance to minimizepatient detection of the threaded fixation structure at superficialimplant locations. In other words, the thread structure may be sized soas not to protrude excessively into the superficial tissues, therebyavoiding skin deformations and potential tissue erosion and damage.

Although lead 14 has been generally described as an electrical lead thatincludes electrodes, lead 14 may, in other embodiments, be a drugdelivery catheter that delivers therapeutic agents to target stimulationsite 18 (FIG. 1A) or occipital nerves 32, 34 or 36. In this case,stimulator 12 is a drug pump that controls the delivery of therapeuticagent to patient 16. The drug delivery catheter embodiment of lead 14may include an exit port for the therapeutic agent that is disposed onany surface of lead 14, adjacent to or within the threaded fixationstructure.

FIG. 2 is a block diagram illustrating various components of implantablestimulator 12 and an implantable lead 14. Stimulator 12 includes therapydelivery module 40, processor 42, memory 44, telemetry module 46, andpower source 47. In some embodiments, stimulator 12 may also include asensing circuit (not shown in FIG. 2). Implantable lead 14 includeselongated member 48 extending between proximal end 48A and distal end48B. Elongated member 48 may also be described as an elongated member.Elongated member 48 may be a cylindrical or may be a paddle-shaped(i.e., a “paddle” lead). Electrodes 50A, 50B, 50C, and 50D (collectively“electrodes 50”) are disposed on elongated member 48 adjacent to distalend 48B of elongated member 48. In the example of FIG. 2, threadedfixation structures are omitted from lead 14 for ease of illustration.

Stimulator 12 delivers stimulation therapy via electrodes 50 of lead 14.In particular, implantable signal generator within therapy deliverymodule 40 delivers electrical signals to patient 16 (FIG. 1A) via atleast some of electrodes 50 under the control of a processor 42. Thestimulation energy generated by therapy delivery module 40 may beformulated as stimulation energy, e.g., for treatment of any of avariety of neurological disorders, or disorders influenced by patientneurological response. The signals may be delivered from therapydelivery module 40 to electrodes 50 via a switch matrix and conductorscarried by lead 14 and coupled to respective electrodes 50.

In some embodiments, electrodes 50 may be ring electrodes. In otherembodiments, electrodes 50 may be segmented or partial ring electrodes,each of which extends along an arc less than 360 degrees (e.g., 90-120degrees) around the circumference of elongated member 48. In embodimentsin which lead 14 is a paddle lead, electrodes 50 may extend along aportion of the periphery defined by elongated member 48. Electrodes 50are electrically coupled to a therapy delivery module 40 of stimulator12 via conductors within elongated member 48.

Electrodes 50 extending around a portion of the circumference of leadbody 48 or along one side of a paddle lead may be useful for providingan electrical stimulation field in a particular direction/targeting aparticular therapy delivery site. For example, in the electricalstimulation application shown in FIG. 1B, electrodes 50 may be disposedalong lead body 48 such that the electrodes face toward occipital nerves32, 34, and/or 36, or otherwise away from the scalp of patient 30. Thismay be an efficient use of stimulation because electrical stimulation ofthe scalp may provide minimally useful therapy, if any, to patient 30.In addition, the use of segmented or partial ring electrodes 50 may alsoreduce the overall power delivered to electrodes 50 by stimulator 12because of the efficient delivery of stimulation to occipital nerves 32,34, and/or 36 (or other target stimulation site) by eliminating orminimizing the delivery of stimulation to unwanted or unnecessaryregions within patient 30. The configuration, type, and number ofelectrodes 28 illustrated in FIG. 2 are merely exemplary.

In embodiments in which electrodes 50 extend around a portion of thecircumference of lead body 48 or along one side of a paddle lead, lead14 may include one or more orientation markers 45 proximate to proximalend 14A that indicate the relative location of electrodes 50.Orientation marker 45 may be a printed marking on lead body 48, anindentation in lead body 48, a radiographic marker, or another type ofmarker that is visible or otherwise detectable (e.g., detectable by aradiographic device) by a clinician. Orientation marker 45 may help aclinician properly orient lead 14 such that electrodes 50 face thedesired direction (e.g., toward occipital nerves 32, 34, and/or 36)within patient 16. For example, orientation marker 45 may also extendaround the same portion of the circumference of lead body 48 or alongthe side of the paddle lead as electrodes 50. In this way, orientationmarker 45 faces the same direction as electrodes, thus indicating theorientation of electrodes 50 to the clinician. When the clinicianimplants lead 14 in patient 16, orientation marker 45 may remain visibleto the clinician.

Stimulator 12 delivers stimulation therapy via electrodes 50 of lead 14.In one embodiment, an implantable signal generator or other stimulationcircuitry within therapy delivery module 40 delivers electrical signals(e.g., pulses or substantially continuous-time signals, such assinusoidal signals) to targets stimulation site 18 (FIG. 1A) via atleast some of electrodes 50 under the control of a processor 42. Thestimulation energy generated by therapy delivery module 40 may beformulated as stimulation energy, e.g., for treatment of any of avariety of neurological disorders, or disorders influenced by patientneurological response. The signals may be delivered from therapydelivery module 40 to electrodes 50 via a switch matrix and conductorscarried by lead 14 and electrically coupled to respective electrodes 50.The implantable signal generator may be coupled to power source 47.Power source 47 may take the form of a small, rechargeable ornon-rechargeable battery, or an inductive power interface thattranscutaneously receives inductively coupled energy. In the case of arechargeable battery, power source 47 similarly may include an inductivepower interface for transcutaneous transfer of recharge power.

Processor 42 may include a microprocessor, a controller, a DSP, an ASIC,an FPGA, discrete logic circuitry, or the like. Processor 42 controlsthe implantable signal generator within therapy delivery module 40 todeliver stimulation therapy according to selected stimulationparameters. Specifically, processor 42 controls therapy delivery module40 to deliver electrical signals with selected amplitudes, pulse widths(if applicable), and rates specified by the programs. In addition,processor 42 may also control therapy delivery module 40 to deliver thestimulation signals via selected subsets of electrodes 50 with selectedpolarities. For example, electrodes 50 may be combined in variousbipolar or multi-polar combinations to deliver stimulation energy toselected sites, such as nerve sites adjacent the spinal column, pelvicfloor nerve sites, or cranial nerve sites.

In addition, processor 42 may control therapy delivery module 40 todeliver each signal according to a different program, therebyinterleaving programs to simultaneously treat different symptoms orprovide a combined therapeutic effect. For example, in addition totreatment of one symptom such as sexual dysfunction, stimulator 12 maybe configured to deliver stimulation therapy to treat other symptomssuch as pain or incontinence.

Memory 44 of stimulator 12 may include any volatile or non-volatilemedia, such as a RAM, ROM, CD-ROM, NVRAM, EEPROM, flash memory, and thelike. In some embodiments, memory 44 of stimulator 12 may store multiplesets of stimulation parameters that are available to be selected bypatient 16 or a clinician for delivery of stimulation therapy. Forexample, memory 44 may store stimulation parameters transmitted byclinician programmer 26 (FIG. 1A). Memory 44 also stores programinstructions that, when executed by processor 42, cause stimulator 12 todeliver stimulation therapy. Accordingly, computer-readable mediastoring instructions may be provided to cause processor 42 to providefunctionality as described herein.

In particular, processor 42 controls telemetry module 170 to exchangeinformation with an external programmer, such as clinician programmer 26and/or patient programmer 28 (FIG. 1A), by wireless telemetry. Inaddition, in some embodiments, telemetry module 46 supports wirelesscommunication with one or more wireless sensors that sense physiologicalsignals and transmit the signals to stimulator 12.

In some embodiments, where lead 14 is a drug delivery catheter, therapydelivery module 40 may include a fluid pump or other release mechanismto dispense a therapeutic agent through lead 14 and into patient 16.Therapy deliver module 40 may also, in this case, include a fluidreservoir which contains the therapeutic agent. Possible therapeuticagents may include pharmaceutical agents, insulin, a pain relievingagent or a gene therapy agent. Refilling the fluid reservoir may beaccomplished by inserting the needle of a syringe through the skin ofpatient 16 and into a refill port in the housing of stimulator 12. Inaddition, more than one lead may be coupled to therapy delivery module40.

FIGS. 3A and 3B are perspective drawings of a sheath that covers a leadprior to implantation and removed after the lead is correctly positionedin a patient, which includes a lead that includes a threaded fixationstructure. As shown in FIG. 3A, lead 52 is capable of deliveringelectrical stimulation to numerous tissue sites within patient 16. Lead52 may be an embodiment of any lead described herein, including lead 14.Prior to delivering stimulation, elongated member 54 of lead 52 iscovered completely around the longitudinal outer surface with sheath 58.Sheath 58 may be constructed to protect electrodes 56 and threadedfixation structure 57 from implantation stresses or damage of adjacenttissues. In addition, sheath 58 may be a restraint mechanism that keepsthreaded fixation structure 57 from being deployed until the clinicianremoved the sheath. Electrodes 56 are typically ring electrodes, butother types of electrodes may be used. For example, segmentedelectrodes, or multiple electrodes around the circumference of elongatedmember 54 may be employed. Alternatively, lead 52 may be in anon-circular shape, such as a rectangular paddle lead. In someembodiments, lead 52 may also include one or more radio-opaque markersthat allow the clinician to image the lead in real time to determine theexact position of the lead within patient after rotating the lead.

Sheath 58 may be constructed of a flexible polymer that provides asmooth interface between the sheath and elongated member 54. Sheath 58may be dimensioned just larger than elongated member 54, or the sheathmay be shrunk to fit elongated member 54 snugly for implantation. Insome embodiments, sheath 58 may constructed to assist the clinician inguiding lead 52 within patient 16. In this case, sheath 58 may be rigidor semi-rigid and similar to a lead introducer or a cannula introductiondevice.

FIG. 3B shows lead 52 with sheath 58 being removed from elongated member54 in the direction of the arrow. Once lead 52 is positioned such thatelectrodes 56 are adjacent to a target tissue for stimulation, theclinician may begin removing lead 52 as shown. As sheath 58 is removed,threaded fixation structure 57 is exposed to the adjacent tissue to fixelongated member 54 in position. In other embodiments, the clinician mayremove sheath 58 in sections as fixation elements need to be deployed oras necessary to ensure proper fixation within patient 16. As will bedescribed in detail below, threaded fixation structure 57 may havedifferent dimensions, sizes, locations, and properties than shown inFIGS. 3A and 3B.

FIGS. 4A-4C are perspective drawings illustrating exemplary stimulationleads with varying configurations of threaded fixation mechanisms. Asshown in FIG. 4A, lead 60 includes elongated member 62, electrodes 64,tapered tip 68, and threaded fixation structure 70. The distal end oflead 60 is shown. Elongated member 62 is substantially cylindrical inshape, but the elongated member may also be configured into any othershape. Electrodes 64 are ring electrodes disposed at the distal end ofelongated member 62. At the distal tip of lead 60, tapered, conical tip68 is attached to, or integrally formed with, elongated member 62.Threaded fixation structure 70 is disposed distal to electrodes 64 andaround the outer surface of tapered tip 68.

Tapered tip 68 is formed in the shape of a cone to facilitate thetunneling of lead 60 through tissue in order to reach the target tissue.Threaded fixation structure 70 is disposed around the outer surface oftapered tip 68 from adjacent to the distal end of the tapered tip to thedistal end of elongated member 62. In this manner, threaded fixationstructure 70 engages with the adjacent tissue of patient 16 as taperedtip 68 pierces through the tissue. As a user, e.g., a clinician, rotateslead 60, threaded fixation structure 70 advances the lead through theadjacent tissue and moves electrodes 64 increasingly closer to a targettissue with each turn of the lead. In other embodiments threadedfixation structure 70 may only be disposed along a portion of taperedtip 68.

Threaded fixation structure 70 may be constructed of a material similarto or different from elongated member 62 or tapered tip 68. The materialof threaded fixation structure 70 may be substantially biologicallyinert, e.g., biocompatible, and may include any of metals, metal alloys,composites, or polymers. Some example materials may include stainlesssteel, titanium, nitinol, polypropylene, polyurethane, polycarbonate,polyethylene, nylon, silicone rubber, orexpanded-polytetrafluoroethylene. The material selection of threadedfixation structure 70 may be based upon whether the structure is desiredto be rigid, semi-rigid, or flexible properties, which could affect theengagement of the structure to the adjacent material. In addition,threaded fixation structure 70 may be a combination of differentmaterials depending on the implantation site. For example, threadedfixation structure 70 may have a flexible distal portion that changes toa rigid portion for precise engagement with the adjacent tissue.Threaded fixation structure 70 may be adhered to tapered tip 68 througha glue, an epoxy, welding, soldering, or any other attachment mechanism.In other embodiments, threaded fixation structure 70 may be an overmoldthat is fitted to a snug fit around elongated member 62. Alternatively,threaded fixation structure 70 may be formed with tapered tip 68.

In addition, threaded fixation structure 70 may have a cross-sectionalshape configured to assist the advancement of lead 60 through theadjacent tissue. The cross-sectional shape of each thread may generallybe a triangle, but other shapes are possible. For example, thecross-sectional shape of threaded fixation structure 70 may be a roundedtriangle, a semi-circle, a square, a rectangle, a trapezoid, or anyother shape desired by the clinician. In addition, the cross-sectionalshape may be angled in a direction non-perpendicular to the outersurface of tapered tip 68. For example, threaded fixation structure 70may be tilted toward the proximal end of lead 60. In other words, theangle between the outer surface of tapered tip 68 and the proximal sideof threaded fixation structure 70 may be less than 90 degrees.Alternatively, the angle between the outer surface of tapered tip 68 andthe proximal side of threaded fixation structure 70 may be greater than90 degrees.

Threaded fixation structure 70 may also be configured to advance throughtissue at a predetermined rate or extend into the tissue a predetermineddistance. The pitch of threaded fixation structure 70 may be defined bythe distance lead 60 is advanced with each full 360 degree rotation ofthe lead, i.e., the axial distance between two peaks of the threadedfixation structure. Threaded fixation structure 70 may have a pitchbetween approximately 0.5 millimeters (mm) and 3 mm. The pitch may beless than approximately 0.5 mm or greater than 3 mm. The height ofthreaded fixation structure 70 is the distance between the outer surfaceof tapered tip 68 and the top edge of the threaded fixation structure.Generally, the height is between approximately 0.1 mm and 3 mm. However,other embodiments of threaded fixation structure 70 may include heightssmaller than approximately 0.1 mm or greater than 3 mm. While threadedfixation structure 70 may have a constant height, the threaded fixationstructure may increase in height as the threaded fixation structuremoves away from the distal end of tapered tip 68. Generally, elongatedmember 62 may have an outside diameter between approximately 0.5 mm and5 mm. The wall thickness of elongated member 62 may be betweenapproximately 0.1 mm and 2 mm. In addition, the ratio of diameter tothread height may be between approximately 1 and 50, depending on theapplication of lead 60.

FIG. 4B shows lead 72, which is an embodiment of lead 60 (FIG. 4A). Lead72 includes elongated member 74, electrodes 76, tapered tip 80, andthreaded fixation structure 82. Lead 72 differs from lead 60 in theshape of tapered tip 80. While tapered tip 68 is constructed as a coneshape, tapered tip 80 is a parabolic shape with an atraumatic, roundeddistal end. Tapered tip 80 may be beneficial if the clinician does notwant a tip that may damage adjacent tissue during extreme bends ofelongated member 74. In other embodiments, tapered tip 80 may beconfigured into a different shape. For example, tapered tip 80 may becurved in any parabolic shape different from that shape of the taperedtip shown in FIG. 4B. In addition, tapered tip 80 may be asymmetrical orbent in a predetermined direction to facilitate creating a curved pathfor lead 72.

FIG. 4C illustrates lead 84 with threaded fixation structure 90 disposedproximal to electrodes 88. Lead 84 includes elongated member 86,electrodes 88 and threaded fixation structure 90. Threaded fixationstructure 90 is disposed around the longitudinal outer surface ofelongated member 86, proximal to the location of electrodes 88. In otherembodiments, threaded fixation structure 90 may be disposed around thelongitudinal outer surface of elongated member 86 at a location distalto electrodes 88. The distal position of threaded fixation structure 90may be instead of or in addition to the proximal position of thethreaded fixation structure.

Threaded fixation structure 90 may include any number of turns aroundelongated member 86. For example, threaded fixation structure 90 mayinclude 3 complete turns as shown in FIG. 4C. However, threaded fixationstructure 90 may include more than 3 or less than 3 turns, as desired bythe clinician for a particular implantation site. In addition, threadedfixation structure 90 may include partial turns, or even continuousstructures with less than one complete turn. In other embodiments,multiple threaded fixation structures 90 may be disposed proximal to ordistal to electrodes 88. In alternative embodiments, lead 84 may includea tip that has a threaded fixation structure such as tapered tips 68 and80 of leads 60 and 72, respectively.

Threaded fixation structure 90 may be constructed of a material similarto or different from elongated member 86. The material of threadedfixation structure 90 may be substantially biologically inert, e.g.,biocompatible, and may include any of metals, metal alloys, composites,or polymers. Some example materials may include stainless steel,titanium, nitinol, polypropylene, polyurethane, polycarbonate,polyethylene, nylon, silicone rubber, orexpanded-polytetrafluoroethylene. The material selection of threadedfixation structure 90 may be based upon whether the structure is desiredto be rigid, semi-rigid, or flexible properties. Threaded fixationstructure 90 may be adhered to elongated member 86 through a glue, anepoxy, welding, soldering, or any other attachment mechanism. In otherembodiments, threaded fixation structure 90 may be an overmold that isfitted to a snug fit around elongated member 86. Alternatively, threadedfixation structure 90 may be integrally formed with elongated member 86,e.g., by injection molding and/or insert molding.

In addition, threaded fixation structure 90 may have a cross-sectionalshape configured to assist the advancement of lead 84 through theadjacent tissue. The cross-sectional shape may generally be a triangle,but other shapes are possible. For example, the cross-sectional shape ofthreaded fixation structure 90 may be a rounded triangle, a semi-circle,a square, a rectangle, a trapezoid, or any other shape desired by theclinician. In addition, the cross-sectional shape may be angled in adirection non-perpendicular to the outer surface of elongated member 86.For example, threaded fixation structure 90 may be tilted toward theproximal end of lead 84. In other words, the angle between the outersurface of elongated member 86 and the proximal side of threadedfixation structure 90 may be less than 90 degrees. Alternatively, theangle between the outer surface of elongated member 86 and the proximalside of threaded fixation structure 90 may be greater than 90 degrees.

Threaded fixation structure 90 may also be configured to advance throughtissue at a predetermined rate or extend into the tissue a predetermineddistance. The pitch of threaded fixation structure 90 may be defined bythe distance lead 84 is advanced with each full 360 degree rotation ofthe lead, i.e., the axial distance between two peaks of the threadedfixation structure. Threaded fixation structure 90 may have a pitchbetween approximately 0.5 millimeters (mm) and 3 mm. In someembodiments, the pitch may be less than approximately 0.5 mm or greaterthan 3 mm. The height of threaded fixation structure 90 is the distancebetween the outer surface of elongated member 86 and the top edge of thethreaded fixation structure. Generally, the height is betweenapproximately 0.1 mm and 3 mm. However, other embodiments of threadedfixation structure 90 may include heights smaller than approximately 0.1mm or greater than 3 mm. As threaded fixation structure 90 increases inheight, the surface area of the threaded fixation structure increases aswell. A larger surface area of threaded fixation structure 90 mayincrease the axial force lead 84 may be able to incur without allowingthe lead to migrate in the direction of the axial force. In other words,a larger height of threaded fixation structure 90 may be desired incases where lead 84 is subjected to greater movement. While threadedfixation structure 90 may have a constant height, the threaded fixationstructure may increase in height as it moves towards the proximal end ofthe threaded fixation structure. Elongated member 62 may have an outsidediameter between approximately 0.5 mm and 5 mm. The wall thickness ofelongated member 62 may be between approximately 0.1 mm and 2 mm. Inaddition, the ratio of diameter to thread height may be betweenapproximately 1 and 50, depending on the application of lead 60.

Implantation of all leads 60, 72, and 84, may vary depending on thetarget stimulation site within patient 16 or implant preferences of theclinician. For example, a sheath (shown in FIGS. 3A and 3B) may be usedto cover any threaded fixation structures to allow insertion of the leadwithout requiring rotation of the lead. Upon positioning the lead nearthe stimulation site, the clinician may remove the sheath and beginrotating the lead to engage to recently exposed threaded fixationstructure. Alternatively, the clinician may guide and rotate the leadthrough a substantial length of the insertion of the lead without theuse of a sheath.

FIGS. 5A-5B are perspective drawings illustrating exemplary stimulationleads with varying threaded fixation mechanisms over electrodes of thelead. As shown in FIG. 5A, lead 92 includes elongated member 94,electrodes 96, and threaded fixation structure 98, a fixation structure.Threaded fixation structure 98 is shown to be disposed around the sameportion of elongated member 94 that includes electrodes 96. In thismanner, threaded fixation structure 98 is located over a portion of thesurface of each electrode 96 as the threaded fixation structure rotatesfrom the proximal end of the threaded fixation structure to the distalend of the threaded fixation structure. Utilizing threaded fixationstructure 98 over electrodes 96 may provide for reduced movement ofelectrodes 96 with respect to the target tissue, compared to threadedfixation structures located elsewhere along the longitudinal outersurface of lead 92. Threaded fixation structure 98 may be constructedsimilar to and have similar physical properties of threaded fixationstructure 90 of FIG. 4C. Threaded fixation structure 98 may attached toelectrodes 96 with an adhesive or other bonding technique, while someembodiments may not have the threaded fixation structure attached to theelectrodes.

While threaded fixation structure 98 is shown to be substantiallydisposed around the entire portion of elongated member 94 that includeselectrodes 96, the threaded fixation structure may also be disposedfurther in the proximal or distal direction along the elongated member.In some embodiments, threaded fixation structure 98 may only be disposedon a portion of the surface including electrodes 96. In other words,threaded fixation structure 98 may not be disposed around all electrodes96, e.g., the threaded fixation structure may only be disposed aroundthe proximal two electrodes. In other embodiments, lead 92 may includethreaded fixation structure 98 at locations along elongated body similarto leads 60, 72, or 84 of FIGS. 4A, 4B, and 4C, respectively.

FIG. 5B shows lead 100 that is substantially similar to lead 92 of FIG.5A. Lead 100 includes elongated member 102, electrodes 104, and threadedfixation structures 106A, 106B, 106C, 106D and 106E (collectively“threaded fixation structures 106). Threaded fixation structures 106 aredisposed at the portion of elongated member 102 which also includeselectrodes 104. However, none of threaded fixation structures 106 arelocated over the surface of any of electrodes 104. Instead, each ofthreaded fixation structures 106 are only attached to elongated member102 and stop before covering any portion of electrodes 104. In otherwords, threaded fixation structures 106 may be substantially similar tothreaded fixation structure 98 of FIG. 5B, but have any portion of thethreaded fixation structure over electrodes 96 removed. In this manner,threaded fixation structures 106 are arranged in sections to avoidinterference with the electrical field produced by electrodes 104 thatprovides therapy to the target tissue of patient 16. Threaded fixationstructures 106 may be constructed similar to and have physicalproperties similar to threaded fixation structure 90 of FIG. 4C. In someembodiments, one or more of threaded fixation structures 106 may beconstructed of different materials to the other threaded fixationstructures.

Threaded fixation structures 106B-D are located between electrodes 104,threaded fixation structure 106A is disposed proximal to electrodes 104and threaded fixation structure 106E is disposed distal to theelectrodes. In some embodiments, threaded fixation structure 106A mayinclude more turns and be disposed along a greater proximal portion ofelongated member 102. Alternatively, threaded fixation structure 106Emay include more turns and be disposed along a greater distal portion ofelongated member 102. In other embodiments, one or more of threadedfixation structures 106 may not be included in lead 100. For example,lead 100 may only include threaded fixation structures 106A-C. Inadditional embodiments, lead 100 may include threaded fixationstructures at locations along elongated body similar to leads 60, 72, or84 of FIGS. 4A, 4B, and 4C, respectively.

FIG. 6 is a perspective drawing illustrating lead 108 with threadedfixation structure extending from the distal end of the lead to alocation proximate to electrodes 112. As shown in FIG. 6, lead 108includes elongate member 110, electrodes 112, tapered tip 114, andthreaded fixation structure 116. Threaded fixation structure begins atthe distal tip of tapered tip 114 and continues to wrap around elongatemember 110 past electrodes 112 to a location of the electrode memberproximal to the electrodes. Lead 108 may be a combination of threadedfixation structures described with respect to leads 60, 72, 84, 92, or100 of FIGS. 4 and 5. In addition, threaded fixation structure 116 mayhave similar properties to any of threaded fixation structures 70, 82,90, 98, or 106. In other embodiments threaded fixation structure 116 maybe broken into two or more threaded fixation structures at any locationalong tapered tip 114 or elongated member 110, including threadedfixation structures that do not cover the surface of electrodes 112. Inalternative embodiments, lead 108 may include threaded fixationstructures at the proximal and/or intermediate locations of elongatemember 110 instead of or in addition to threaded fixation structure 116.

FIG. 7 is a perspective drawing illustrating lead 118 that includes areinforcement member. Lead 118 is substantially similar to lead 108 ofFIG. 6 and includes elongate member 120, electrodes 122, tapered tip124, and threaded fixation structure 126. In contrast to lead 108, lead118 includes helical reinforcement member 128 which resides withinelongated member 120. Helical reinforcement member 128 is provided toadd torsional rigidity to lead 118 which resists twisting of elongatedmember 120 when the clinician rotates the lead to engage threadedfixation structure 126.

Helical reinforcement member 128 may be provided in a variety ofmethods. First, helical reinforcement member 128 may be a metal orpolymer wire. Second, helical reinforcement member 128 may be a metal orpolymer ribbon that creates a substantially contiguous cylinder. Otherfibers, materials, or members may be used to construct helicalreinforcement member 128, in some embodiments. While helicalreinforcement member 128 is shown as extending within elongate member120 in a direction opposite threaded fixation structure 126, someembodiments may employ the helical reinforcement member in the samedirection as the threaded fixation structure. Alternatively, helicalreinforcement member 128 may include two helical reinforcement membersin which one helical reinforcement member is arranged in one directionand the second helical reinforcement member is arranged in a seconddirection opposite the first direction. Helical reinforcement member 128may extend throughout the entire length of lead 118 or only a smallportion of the lead.

FIGS. 8A and 8B are perspective drawings illustrating exemplarystimulation leads with foldable threads. FIG. 8A illustrates lead 130prior to the removal of sheath 138. Lead 130 includes elongated member132, electrodes 134, threaded fixation structure 136, and sheath 138.Lead 130 may be similar to any of leads 60, 72, 84, 92, 100, 108 or 118;however, threaded fixation structure 136 is foldable, or compliant, suchthat sheath 138 prevents the threaded fixation structure from extendingaway from elongated member 132. While threaded fixation structure 136 isshown to be disposed around the portion of elongated member 132 thatincludes electrodes 134, the threaded fixation structure may be disposedat any portion of the elongated member as described herein.

Sheath 138 is provided to facilitate implantation of lead 130. Withsheath 138 covering elongated member 132 and collapsing threadedfixation structure 136, the diameter of lead 130 is smaller to allow theclinician to push the lead through a lead introducer (not shown) orthrough tissue of patient 16. Once the clinician inserts lead 130 to thedesired position, sheath 138 is removed to expose threaded fixationstructure 136 to the adjacent tissue. Threaded fixation structure 136extends away from the outer surface of elongated member 132 to theoriginally formed threaded fixation structure dimensions. Rotating lead130 may help threaded fixation structure 136 to extend away from thesurface of elongated member 132 and engage the surrounding tissue. Theextended angle of threaded fixation structure 136 may be less than 90degrees between the outer surface of elongated member 132 and theproximal surface of the threaded fixation structure. While threadedfixation structure 136 is foldable towards the proximal end of lead 130,the threaded fixation structure may be foldable towards the distal endof the lead in other embodiments.

Threaded fixation structure 136 may be constructed of any bendable,pliable, elastic, or superelastic material that is biocompatible. Forexample, a polymer such as expanded-polytetrafluoroethylene or a shapememory metal alloy such as nitinol may be used to construct threadedfixation structure 136. Sheath 138 may be constructed of a thin polymermembrane that may slide over the surface of elongated member 132 andthreaded fixation structure 136 while maintaining sufficientcircumferential stiffness that retains the threaded fixation structurebefore deployment. Sheath 138 may be initially configured to coverelongated member 132 and threaded fixation structure 136 by sliding thesheath from the distal end of lead 130 to the proximal end of the lead.Alternatively, sheath 138 may loosely cover lead 130 and be heated toshrink the circumference of the sheath and collapse threaded fixationstructure 136.

FIG. 8B shows lead 130 with sheath 138 being removed in the proximaldirection of arrow 140. The distal portion of threaded fixationstructure 136 has already extended away from elongated member 132 in thedirection of arrow 142. The proximal portion of threaded fixationstructure, indicated by arrow 144, is still restricted by sheath 138that has not been fully removed. Once sheath 138 is fully removed fromlead 130, the clinician may rotate the lead to engage threaded fixationstructure 136 with the adjacent tissue. In addition, once sheath 138 isremoved from lead 130, the clinician may not be able to slide the sheathback over threaded fixation structure 136.

In alternative embodiments, sheath 138 may not be necessary for threadedfixation structure 136 to fold down against elongated member 132.Threaded fixation structure 136 may fold down from force from adjacenttissue when the clinician inserts lead 130 into patient 16. When lead130 is properly positioned, the clinician may pull back on the lead tocause threaded fixation structure 136 to engage with the adjacent tissueand extend the threaded fixation structure away from elongated member132. The clinician can then begin to rotate lead 130 to screw the leadinto the tissue and secure electrodes 134 to the desired location.

FIG. 9 is a flow diagram illustrating an exemplary process for securinga threaded lead to a tissue of a patient. Any of leads 60, 72, 84, 92,100, 108 or 118, or 130 may be implanted with this procedure, but lead60 will be used as an example. The clinician beings by inserting thelead introducer into the target stimulation site of patient 16 (146).Next, the clinician inserts lead 60 into the lead introducer until thelead is positioned correctly (148). The clinician then withdraws thesheath that covers lead 60 (150) and rotates the lead in the directionof threaded fixation structure 68, e.g., clockwise, to secure the leadat the target tissue (152). If lead 60 is not correctly placed (154),the clinician continues to rotate the lead (152). If lead 60 ispositioned correctly (154), the clinician may attach the proximal end ofthe lead to the stimulator and proceed with beginning therapy (156).

In some embodiments, the clinician may not need to remove a sheath toexpose the threaded fixation structure. In other embodiments, theclinician may require a keyed stylet or other device that engages intothe distal end of the lead and locks into interior grooves or teeth tofacilitate the rotation of the lead and engagement of the threadedfixation structure. Alternatively, the stylet may be inserted through achannel extending within lead 60 that attaches to grooves, slots, orteeth near the proximal end of the lead to facilitate lead rotation thatengages the threaded fixation structure to the adjacent tissue.

FIG. 10 is a flow diagram illustrating an exemplary process for removinga threaded lead from a tissue of a patient. Any of leads 60, 72, 84, 92,100, 108 or 118, or 130 may be implanted with this procedure, but lead60 will be used as an example. After stimulation therapy has beencompleted or lead 60 needs to be removed for any other reason, theclinician may ready patient 16 for removal of the lead from stimulator12 (158). If the threaded fixation structure is foldable (160), theclinician inserts a sheath down to the proximal end of the threadedfixation structure (162). If the threaded fixation structure of lead 60is not foldable, or the sheath has been inserted to the foldablethreads, the clinician begins to rotate the lead in the oppositedirection of the threaded fixation structure, e.g., counter-clockwise(164). If the threaded fixation structure is not released from tissue(166), the clinician continues to rotate lead 60 (164). If the threadedfixation structure has been released from tissue (166), the clinicianmay pull lead 60 from patient 16 (168). Releasing the threaded fixationstructure from the tissue may include either backing the threadedfixation structure into the sheath such that the structure folds underthe sheath or rotating the lead enough that the threaded fixationstructure is free from being engaged from any tissue of patient 16.

Similar to FIG. 9, some embodiments may require that the clinician use akeyed stylet or other device that engages into the distal end of thelead and locks into interior grooves or teeth to facilitate the rotationof the lead and disengagement of the threaded fixation structure.Alternatively, the stylet may be inserted through a channel extendingwithin lead 60 that attaches to grooves, slots, or teeth near theproximal end of the lead to facilitate lead rotation that disengages thethreaded fixation structure from the adjacent tissue.

FIG. 11 is a method of implanting a lead in patient 12 with a differentthreaded fixation structure than the leads implanted in with thetechnique of FIG. 9. Any of leads 60, 72, 84, 92, 100, 108 or 118, or130 with a foldable threaded fixation structure may be implanted withthis procedure, but lead 130 will be used as an example. The clinicianbeings by inserting the lead introducer into the target stimulation siteof patient 16 (169), which causes threaded fixation structure 136 tofold down against the surface of lead 130. Next, the clinician insertslead 130 into the lead introducer until the lead is positioned correctly(171). The clinician then removes the lead introducer that covers lead130 (173) and pulls back on the lead to engage, or extend, the foldedthreaded fixation structure with the adjacent tissue (175). Theclinician then rotates the lead in the direction of threaded fixationstructure 136, e.g., clockwise, to secure the lead at the target tissue(177). If lead 130 is not correctly placed (179), the cliniciancontinues to rotate the lead (177). If lead 130 is positioned correctly(179), the clinician may attach the proximal end of the lead to thestimulator and proceed with beginning therapy (181).

In some embodiments, the clinician may be able to insert lead 130directly into patient 16 without the use of a lead introducer. In thiscase, foldable threaded fixation structure 136 folds down with the forceof the adjacent tissue as lead 130 is inserted into patient 16. In otherembodiments, the clinician may require a keyed stylet or other devicethat engages into the distal end of the lead and locks into interiorgrooves or teeth to facilitate the rotation of the lead and engagementof the threaded fixation structure. Alternatively, the stylet may beinserted through a channel extending within lead 130 that attaches togrooves, slots, or teeth near the proximal end of the lead to facilitatelead rotation that engages the threaded fixation structure to theadjacent tissue.

FIGS. 12A and 12B are perspective drawings illustrating exemplarymedical catheters with a helical threaded structure. Threaded fixationstructures 174 and 184 may be similar to the threaded fixationstructures of any of leads 60, 72, 84, 92, 100, 108 or 118, or 130.However, a conduit is used to deliver a therapeutic agent to the tissueinstead of electrodes that deliver stimulation. FIG. 12A shows lead 170that includes elongated member 172, threaded fixation structure 174,conduit 176, and exit port 178. Threaded fixation structure 174 isdisposed about the outer surface of elongated member 172 at the distalend of the elongated body. A drug pump may be attached to the proximalend of lead 170 for delivering a therapeutic agent through conduit 176and out of exit port 178 into the adjacent target tissue. Conduit 176resides within elongated member 172, and may or may not have a commoncentral axis to the elongated member. In other embodiments, more thanone threaded fixation structure 174 may be provided to secure thelocation of lead 170 and ensure that the therapeutic agent is deliveredto the appropriate tissue of patient 16.

FIG. 12B shows lead 180 which is similar to lead 170 of FIG. 12A. Lead180 includes elongated body 182, threaded fixation structure 184,conduit 186, and exit port 188. Exit port 188 is disposed on alongitudinal outer surface of elongated member 182, within threadedfixation structure 184. Conduit 186 resided within elongated member 182,and may or may not have a common central axis with the elongated member.In other embodiments, exit port 188 may be located outside of threadedfixation structure 184 either distal to or proximal to the threadedfixation structure. In alternative embodiments, conduit 186 may be influidic communication with more than one exit port, where the multipleexit ports are located at various longitudinal or circumferentialpositions of elongated member 182 or in the axial surface of theelongated member. In addition, lead 180 may include multiple conduitswithin elongated member 182.

FIGS. 13A and 13B are cross-sectional end views of a keyed stylet 200and a reciprocally keyed medical lead 202. As discussed previously,rotational movement of a lead may be accomplished by simply rotating thelead body. In some embodiments, however, it may be desirable to rotatethe lead body with the aid of a stylet inserted in an inner lumen of thelead body. For example, a stylet may provide added structural integrityrelative to a flexible lead. The stylet may be sized to frictionallyengaged the inner wall of the inner lumen such that rotation of thestylet causes rotation of the lead body. Alternatively, the stylet andthe lead body may be formed with a reciprocal key structure, such as anycombination of slots, grooves, teeth, ribs, rails, or the like.

In the example of FIGS. 13A and 13B, stylet 200 includes a stylet body203 with multiple teeth 204A-204D. The teeth may run longitudinallysubstantially the entire length of the stylet body 203, or be providedonly near a distal end of the stylet body, e.g., over the last 2 to 6centimeters at the distal end of the stylet. In either case, teeth204A-204D may be sized and shaped to engage reciprocal grooves 210A-210Din a lead body 206 of lead 202. The grooves 210A-210D may be formed bymolding, extruding, scribing or other techniques. In any event, teeth204A-204D engage corresponding grooves 210A-210D so that the teeth canbear against the grooves to transmit rotational force from stylet 200 tolead 202.

Also shown in FIG. 13B are representative portions 212A, 212B of athreaded fixation structure. Any thread fixation structure, as describedherein, may be combined with a lead 202 including slots, grooves, or thelike. Moreover, the number of slots or grooves may be subject to widevariation. Also, in some embodiments, lead 202 may include teeth whilestylet 200 includes grooves. The exact combination, arrangement, size,and number of slots, grooves, teeth or the like is subject to variationprovided the lead 202 and stylet 200 include reciprocal structure toimpart rotational movement from the stylet to the lead.

Alternative to keyed stylet 200, a cannula device that is configured tofit around the outside of the lead may be used to rotate the lead andengage the threaded fixation structure. The cannula device may becircumferentially locked to the lead via one or more slots, grooves,teeth, ribs, rails, or the like, disposed on the outside of theelongated member. In some embodiments, the cannula device may use afriction fit to lock to the lead. In either case, the cannula device maybe slid down to the proximal end of the threaded fixation structure orsome other location of the lead that still facilitates rotation of thelead.

A lead including threaded fixation may be useful for various electricalstimulation systems. For example, the lead may be used to deliverelectrical stimulation therapy to patients to treat a variety ofsymptoms or conditions such as chronic pain, tremor, Parkinson'sdisease, multiple sclerosis, spinal cord injury, cerebral palsy,amyotrophic lateral sclerosis, dystonia, torticollis, epilepsy, pelvicfloor disorders, gastroparesis, muscle stimulation (e.g., functionalelectrical stimulation (FES) of muscles) or obesity. In addition, thehelical fixation described herein may also be useful for fixing acatheter, such as a drug deliver catheter, proximate to a target drugdelivery site.

The preceding specific embodiments are illustrative of the practice ofthe invention. It is to be understood, therefore, that other expedientsknown to those skilled in the art or disclosed herein may be employedwithout departing from the invention or the scope of the claims. Forexample, the present invention further includes within its scope methodsof making and using systems and leads for stimulation, as describedherein. Also, the leads described herein may have a variety ofstimulation applications, as well as possible applications in otherelectrical stimulation contexts, such as delivery of cardiac electricalstimulation, including paces, pulses, and shocks.

Many embodiments of the invention have been described. Variousmodifications may be made without departing from the scope of theclaims. These and other embodiments are within the scope of thefollowing claims.

1. A medical lead comprising: an elongated member having a proximal endand a distal end; at least one stimulation electrode disposed closer tothe distal end of the lead than the proximal end of the lead; and atleast one threaded structure extending around a portion of an outersurface of the elongated member and configured to engage tissue within apatient to resist migration of the medical lead.
 2. The medical lead ofclaim 1, wherein the portion of the outer surface is proximal to the atleast one stimulation electrode.
 3. The medical lead of claim 1, whereinthe portion of the outer surface is distal to the at least onestimulation electrode.
 4. The medical lead of claim 3, furthercomprising a tapered tip at the distal end of the elongated member,wherein the tapered tip includes the portion.
 5. The medical lead ofclaim 1, wherein the portion of the outer surface includes the at leastone stimulation electrode.
 6. The medical lead of claim 1, wherein aplurality of threaded fixation structures are formed around the portionof the outer surface of the elongated member to simulate a continuousthreaded fixation structure.
 7. The medical lead of claim 1, wherein thethreaded fixation structure is foldable in one direction to allow thethread structure to lay substantially flat against the elongated memberwhen restrained by a sheath.
 8. The medical lead of claim 1, furthercomprising a helical reinforcement member disposed within an innersurface of the elongated member to provide torsional rigidity to theelongated member.
 9. The medical lead of claim 8, wherein the helicalreinforcement member is disposed in a direction different than thedirection of the threaded fixation structure.
 10. The medical lead ofclaim 1, wherein the threaded fixation structure comprises a pitchbetween adjacent threads or approximately 0.5 millimeters (mm) toapproximately 3 mm.
 11. The medical lead of claim 1, wherein thethreaded fixation structure comprises a thread height betweenapproximately 0.1 millimeters (mm) and approximately 3 mm.
 12. Themedical lead of claim 1, wherein the threaded fixation structurecomprises at least one of a biocompatible metal alloy and abiocompatible polymer.
 13. A method comprising: inserting a medical leadinto a patient, wherein the lead comprises at least one stimulationelectrode and at least one threaded fixation structure extending arounda portion of an outer surface of the lead; and rotating the lead toengage the threaded fixation structure with tissue of the patient toresist migration of the lead.
 14. The method of claim 13, furthercomprising removing a sheath from the lead to expose the at least onethreaded fixation structure after the lead is inserted into the patient.15. The method of claim 14, wherein removing the sheath allows the atleast one threaded fixation structure to unfold and extend from thelead.
 16. The method of claim 13, further comprising generatingelectrical stimulation with a stimulator and delivering the electricalstimulation to the patient via the at least one stimulation electrode ofthe lead.
 17. The method of claim 13, further comprising rotating thelead to disengage the threaded fixation structure from the tissue in thepatient.
 18. The method of claim 13, further comprising sliding a sheathover the lead to cover the at least one threaded fixation structure withthe sheath.
 19. The method of claim 18, further comprising removing thelead and sheath from the patient
 20. The method of claim 13, whereininserting a medical lead into a patient comprises forcing the at leastone threaded fixation structure to fold down against the outer surfaceof the lead in a first direction.
 21. The method of claim 20, furthercomprising pulling the lead in the first direction to extend the atleast one threaded fixation structure into the tissue, and whereinrotating the lead causes the at least one threaded fixation structure toadvance the lead in a second direction opposite the first direction. 22.The method of claim 13, further comprising positioning the at least oneelectrode adjacent to at least one of a sacral nerve, a pudendal nerve,a spinal cord, and an occipital nerve.
 23. A system comprising: amedical lead comprising: an elongated member having a proximal end and adistal end; at least one stimulation electrode disposed closer to thedistal end of the lead than the proximal end of the lead; and at leastone threaded structure extending around a portion of an outer surface ofthe elongated member and configured to engage tissue within a patient toresist migration of the medical lead; and a stimulator that deliverselectrical stimulation therapy to a patient via the medical lead withinthe patient.
 24. An apparatus comprising: an elongated member having aproximal end and a distal end; a conduit disposed within the elongatedmember; an exit port disposed on an outer surface of the elongatedmember in fluidic communication with the conduit; and at least onethreaded fixation structure extending around a portion of an outersurface of the elongated member and configured to engage tissue within apatient to resist migration of the medical lead.
 25. The apparatus ofclaim 24, wherein the exit port is disposed on an axial outer surface ofthe distal end of the elongated member.
 26. The apparatus of claim 24,wherein the exit port is disposed on a longitudinal outer surface of theelongated member.
 27. The apparatus of claim 26, wherein the at leastone threaded fixation structure is disposed at least one of proximal tothe exit port and distal to the exit port.
 28. The apparatus of claim24, wherein the at least one threaded fixation structure is foldable inone direction to allow the thread structure to lay substantially flatagainst the elongated member when restrained by a sheath.
 29. Theapparatus of claim 24, further comprising a helical reinforcement memberdisposed within an inner surface of the elongated member to providetorsional rigidity to the elongated member.
 30. The apparatus of claim29, wherein the helical reinforcement member is disposed in a directiondifferent than the direction of the at least one threaded fixationstructure.
 31. The apparatus of claim 24, wherein the threaded fixationstructure comprises a pitch between approximately 0.5 millimeters (mm)and 3 mm.
 32. The apparatus of claim 24, wherein the threaded fixationstructure comprises a thread height between approximately 0.1millimeters (mm) and 3 mm.
 33. The apparatus of claim 24, wherein thethreaded fixation structure comprises at least one of a biocompatiblemetal alloy and a biocompatible polymer.
 34. The apparatus of claim 24,wherein the conduit delivers a therapeutic agent to the patient via theexit port.